Contamination detection and quantitation requirements have become increasingly important, particularly with the rapid evolution of the highly technical industries. For example, the semiconductor industry has developed technology for precisely producing microelectronic devices. In order to reliably produce such products, highly stringent contamination standards must be maintained in the production facilities.
In an effort to control and minimize contamination in crucial stages of a production process, "cleanrooms" are frequently used. A cleanroom is a room in which the air filtration, air distribution, utilities, materials of construction, equipment, and operating procedures are specified and regulated to control airborne particle concentrations to meet appropriate airborne particulate cleanliness classifications. Existing inspection and sampling techniques are inadequate for quickly verifying cleanliness. IES-RP-CC-018-89-T, Sec. 6, p. 7.
Currently there are two primary types of test procedures which are recommended for detecting particles on a cleanroom surface. First, there are visual inspection techniques using ultraviolet or oblique white light. Ultraviolet light is employed to take advantage of the fact that certain organic particles fluoresce. Alternatively, white light is shined towards the test surface at an angle so as to produce reflections which can be visualized. While the white light technique is slightly more sensitive than the ultraviolet technique, they both suffer from the same limitations. These visual inspection techniques only allow a cursory inspection of the surface conditions. They do not provide quantitative data. Also, the visual inspection techniques, at best, only detect particles which are larger than twenty microns. It is often desirable to detect particles which are less than one micron.
The second type of recommended testing procedure involves removing particles from a test surface, by for example, applying a piece of adhesive tape to the test surface. The particles on the tape are then manually quantitated by putting the tape under a microscope and visually counting the particles. This technique allows the detection of particles of approximately five microns or larger. The primary disadvantage of this technique is that it is very time consuming, and that it is highly sensitive to variability between operators. Given the advanced state of technology today, it is surprising that no more advanced techniques for detecting and quantitating contamination on processing surfaces, have been developed to address these fundamental objectives.